This invention relates to an electromagnetic device suitable for a microminiature oscillator or switching device and to a circuit for driving the electromagnetic device.
In recent years, portable telephones have been surprisingly popularized, and those designed to inform users of the ringing of telephones through oscillations have been chiefly used for the extension of user strata and the convenience of users. Such a portable telephone is constructed so that an eccentric weight is attached to the main shaft of a motor housed in a telephone body and is rotated by the rotation of the motor driven simultaneously with the reception of a call signal, and a difference in position between the main shaft and the eccentric weight is converted into an oscillation to transmit this oscillation to a user.
For the portable telephone of this type, a coreless-type motor is usually used (refer to, for example, Japanese Patent Preliminary Publication No. Hei 4-275046). This motor, however, not only is complicated in structure and high in cost, but also causes a forced rotation because it is used in a state where the eccentric weight is attached to a motor shaft. Hence, one-sided wear of bearings and the deformation of a rotary shaft are produced, raising the problem of impairing durability. Furthermore, since a space sufficient to turn the weight must be provided, a relatively large space is required for an oscillation generator. This makes it difficult to achieve compactness of the device. In addition, there is a disadvantage even when the effective utilization of electric power is considered.
A system constructed so that a pulse motor is incorporated and an oscillation pattern can be selected to securely call a mate intended when necessary, is proposed (refer to, for example, Japanese Patent Preliminary Publication No. Hei 5-191334). However, this system has the same problem as in the above case.
It is, therefore, an object of the present invention to provide an electromagnetic device which not only can be manufactured in small size and at a low cost and guarantees high reliability of operation and durability, but also is capable of effectively utilizing electric power and is suitable for an oscillator, and a circuit for driving the electromagnetic device.
The electromagnetic device according to the present invention is provided with a coil bobbin supporting an excitation coil and a U-shaped movable iron piece constructed of a soft magnetic material to have a resilient characteristic that when one side thereof is inserted in and fixed to the coil bobbin in the direction of the axis of the excitation coil, the other side thereof is spaced away from the one side. The other side of the movable iron piece is held to be displaceable against its resilient force by the coil bobbin so that the end of the one side of the movable iron piece is opposite to the end of the other side at a predetermined distance away.
Further, the electromagnetic, device according to the present invention is provided with a coil bobbin supporting an excitation coil; a U-shaped movable iron piece constructed of a soft magnetic material to have a resilient characteristic that when one side thereof is inserted in and fixed to the coil bobbin in the direction of the axis of the excitation coil, the other side thereof is spaced away from the one side; a leaf spring whose base is fastened to the other side of the movable iron piece and whose top extends beyond the end of the other side; and a weight fastened to the top of the leaf spring. The other side of the movable iron piece is held to be displaceable against its resilient force by the coil bobbin so that the end of the one side of the movable iron piece is opposite to the end of the other side at a predetermined distance away.
Still further, the electromagnetic device according to the present invention is provided with a coil bobbin supporting an excitation coil; a U-shaped movable iron piece constructed of a soft magnetic material so that one side thereof is inserted in and fixed to the coil bobbin in the direction of the axis of the excitation coil, while the other side thereof is opposite to the one side at a predetermined distance away; and a U-shaped leaf spring provided along the movable iron piece to have a resilient characteristic that when one side thereof is inserted in and fixed to the coil bobbin in the direction of the axis of the excitation coil, the other side thereof is spaced away from the one side. The other side of the leaf spring is held by the coil bobbin to be displaceable, together with the movable iron piece, against its resilient force.
The electromagnetic device of the present invention is provided with a coil bobbin supporting an excitation coil; a U-shaped movable iron piece constructed of a soft magnetic material, engaging with the coil bobbin to be displaceable so that one side thereof is inserted in and fixed to the coil bobbin in the direction of the axis of the excitation coil, while the other side thereof is opposite to the one side at a predetermined distance away; and a resilient member interposed between the opposite sides of the movable iron piece, pressing the opposite sides so that they are spaced away from each other.
According to the present invention, the top of at least one of the opposite sides of the movable iron piece is bent toward the other so that a flux linkage is increased, or an iron piece is fastened to at least one of the opposite sides and is configured to project toward the other so that the flux linkage is increased.
According to the present invention, the electromagnetic device is further provided with an iron core inserted in and fixed to the coil bobbin in the direction of the axis of the excitation coil, having a rising section engaged with the top of one side of the movable iron piece and bent toward the other side so that a flux linkage is increased.
According to the present invention, the electromagnetic device is still further provided with a pair of iron cores inserted in and fixed to the coil bobbin so as to hold one side of the movable iron piece between the iron cores in the direction of the axis of the excitation coil, having a first rising section in which one of the iron cores is engaged with the top of one side of the movable iron piece and is bent toward the other side so that a flux linkage is increased and a second rising section in which the other is adjacent to the first rising section and is bent toward the other side so that the flux linkage is increased.
According to the present invention, the top surface of each of the first and second rising sections is configured by bending each rising section.
According to the present invention, a proper selection is made so that a magnetic path length governed by the U-shaped movable iron piece and the iron cores is 24-36 mm, the cross-sectional area of the movable iron piece is 1.2-3.2 mm2, and the cross-sectional area of each of the iron cores is 2.4-3.6 mm2.
The driving circuit of the electromagnetic device according to the present invention is constructed so that a series circuit including a normally open switch closed for a preset time by a call signal, a power supply, and a current-pulse circuit is connected in series with the excitation coil.
According to the present invention, an arithmetical unit is connected to the current-pulse circuit so that the arithmetical unit is capable of controlling at least one of the conduction time, conduction period, and conduction duration of a pulse current supplied from the current-pulse circuit to the excitation coil.